An image reader is a device for scanning characters, patterns or the like on an original document by an image sensor, converting its optical image into an electrical signal and outputting said electrical signal.
Conventional image readers cannot determine whether an original document has an image thereon. Therefore, image readers, when given a blank document or the reverse face of the document, only output electrical signals representing all most white picture elements.
Image readers are used in a word processing system or filing system as connected to a memory device, printer or the like. When a blank document is included in original documents, the image readers used in the aforesaid system reads the blank document to write its data in the memory device, e.g., an optical disc, thereby causing uneconomical use of the memory. Further, it is uneconomical for the circuit and the recording paper that the image readers serving as a facsimile in combination with a printer and sending/ receiving unit read a blank document to send its data.